Optimal Current Profile Control for Enhanced Repeatability of L-mode and H-mode Discharges in DIII-D

W.P. Wehner, J.E. Barton, E. Schuster, C.T. Holcomb, T.C. Luce, J.R. Ferron, M.L. Walker, D.A. Humphreys, B.G. Penaflor and R.D. Johnson

Fusion Engineering and Design, 123 (2017) 513–517

Abstract

In this work, model-based control techniques are used to obtain target current profiles in low- confinement-mode (L-mode) as well as high-confinement-mode (H-mode) DIII-D discharges. The control problem is formulated as a trajectory optimization problem to search for a feasible path from the expected initial condition to the desired target. The result comprises a sequence of feedforward (open-loop) control requests and a corresponding state evolution from the initial condition to the desired target. On top of this optimal feedforward control sequence a feedback (closed-loop) controller based on a linearized model and optimal control design techniques is added to track the desired state evolution. The effectiveness of the control approach is demonstrated with experiments.